1. Field of the Invention
This invention relates to a method for estimating the shape of a fusion belt in a blast furnace for stabilization of its operation control.
2. Description of the Prior Art
In a blast furnace, iron ore and coke which are charged in alternate layers are reduced by rising reducing gas while they slowly go down the furnace. The ore which has undergone changes in composition by the reduction shows inherent softening and melting points but since the furnace temperature becomes higher in the lower portions of the furnace the ore sooner or later reaches a region of the same temperature level as its softening and melting points. There, the massive layer is not fused immediately but generally softens and melts upon reaching a certain temperature region and then starts to drip, forming molten pig iron and slag. That is, a softened and fused layer of ore exists in a certain locality of the furnace which is generally called "saftening-menting zone" (hereinafter referred to simply as "cohesive zone"). The shape of such a fusion belt in the blast furnace has thus far been in the realm of mere guesswork until recent studies on disassembled blast furnaces, conducted by furnace manufacturers, revealed that the cohesive zone has a large distribution in the vertical direction of the furnace as well as in a transverse sectional area. It has also been revealed that these distributions are closely related to the furnace conditions, showing various patterns depending upon the furnace conditions. A typical pattern is diagrammatically shown in FIG. 1, depicting a blast furnace 1 charged with alternate layers of iron ore 3 (e.g., in the form of pellets or sintered ore) and coke 4, via the top 1a of the furnace 1. The reference numeral 6 indicates a massive zone of the descending layers upstream of a cohesive zone 7 which is formed in an inverted V-shape in the shaft portion 1b of the furnace 1, molten pig iron and slag dripping through and along a coke layer 5 enveloped by the cohesive zone 7 in a center portion of the furnace. On the other hand, hot blasts admitted through tuyeres or inlets 2 ascend the shaft 1b as indicated by arrows, said hot blasts however being blocked by the cohesive zone 7 which is extremely low in void fraction and gas permeability due to its inherent physical properties. Therefore, the reducing gas which has ascended through the center coke layer 5 is, upon reaching the underside of the melt bonded layer 7, distributed in upward and radial directions as indicated by arrows in FIG. 1. The upwardly distributed gas ascends through the center coke layer 5 along the cohesive zone 7, while the radially distributed gas flows toward the massive zone 6 through openings or slits 7' in the cohesive zone 7. Namely, the cohesive zone 7 has the function of distributing the climbing gas so that the degree of distribution of the gases within the furnace is greatly influenced by the shape, and particularly the distribution, of the cohesive zone 7 itself. For example, in a case where the cohesive zone 7 is maldistributed in the center portion of the furnace, the climbing gas flows take place mainly in the peripheral portions of the furnace. On the other hand, in a case where the cohesive zone 7 is maldistributed in the peripheral portions of the furnace, the gas flows take place mainly in the center portion of the furnace. The reduction of the cohesive zone 7 is accelerated in its peripheral portions by the peripheral gas flows and in the center portion by the center gas flows, not only giving direct influence to the shape of the next melt massive belt but also prevailing as a predominant factor of the reducing process.
In view of these circumstances, it has been found that the shape of the melt mass belt has an important influence on the smooth gravitationally induced descent of the ore burden and the effective distribution of the reduding gas. Therefore it is necessary to maintain the cohesive zone in an appropriate form in order to ensure smooth operation and high productivity of the blast furnace. To this end, the shape of the cohesive zone at any given time has to be grasped and understood precisely, and as soon as possible. However, at the present stage of the art, the shape is usually speculated by estimate calculations based on data of measurements from the outside and in the absence of an established method for dynamically grasping the shape of the cohesive zone in actual furnaces.